What firmware edition/version did you install?
Did you do the "thorough" nvram erase after installing Tomato? Do it now if you didn't, and then re-enter your settings manually.
Did you activate the USB and NTFS support in the GUI, and saved the settings?
What does the GUI say about the drive on the "USB and NAS" page in the "Attached Devices" section?
What does your system log show after you attach the drive, and then after you attempt to mount the drive?